Role of Pt in the Activity and Stability of PtNi/CeO2-Al2O3 Catalysts in Ethanol Steam Reforming for H2 Production

摘要

Hydrogen production from ethanol reforming was investigated on bimetallic PtNi catalysts supported on CeO2/Al2O3. Pt content was varied from 0.5 to 2.5 %. Physico-chemical characterization of the as-prepared and H2-reduced catalysts by TPR, XRD and XPS showed that Pt phase interacted with the Ni and Ce species present at the surface of the catalysts. This interaction leads to an enhancement of the reducibility of both Ni and Ce species. Loadings of Pt higher than 1.0 wt% improved the activity and stability of the Ni/CeO2-Al2O3 catalyst in emanol steam reforming, in terms of lower formation of coke, C2 secondary products and a constant production of CO2 and H2. The amount and type of carbon deposited on the catalyst was analyzed by TG-TPO while the changes in crystalline phases after reaction were studied by XRD. It was found that for Pt contents higher than 1 wt% in the catalysts, a better contact between Pt and Ce species is achieved:* This Pt-Ce interaction facilitates the dispersion of small particles of Pt and thereby improves the reducibility of both Ce and Ni components at low temperatures. In this type of catalysts, the cooperative effect between Pt°, Ni° and reduced Ce phases leads to an improvement in the stability of the catalysts: Ni provides activity in C-C bond breakage, Pt particles enhance the hydrogenation of coke precursors (C_xH_y) formed in the reaction, and Ce increases the availability of oxygen at the surface and thereby further enhances the gasification of carbon precursors.